Bicycle MechanicsBroken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

Typically Shimano is conservative so a 28 tooth cog is likely to work even though they say 27 max. There have been many reports of 30 and even 32T large cogs working with Shimano road derailleurs rated at 27T max.

The most likely problem will be with "wrap capacity". Shimano says the short cage RD-6600 will wrap up a maximum of 29T while your proposed gearing requires 33T (50-34+ 28-11 = 33) of wrap. If you size the chain to just allow big-big (which is essential for safety) you won't be able to use the 34T chainring with the smallest two or three cogs without the chain going too slack. This isn't a big deal but be aware of the limitation.

I went to a 30 IRD with no problem, but the is a fair amount of extension in my cross RD bracket; I ended up with more than 6mm between the pulley and 30 cog..sweet. I'm sure it could have taken a 32T with a little b screw adjustment. Perfect shifts. However, the chain length and slack issue is what you'll have to be cautious about.

I ran an 11-32 cassette with 38/48 set up on my cross bike for a while (mainly to get my Clydesdale butt up some big hills). I could use every combination I wanted except 48-32, which was a cross chain anyway. I never tried 38-11. Give it a shot.